Caffeine and nicotine

This explains a lot, if it's true; posted on alt.coffee by one CmdrJoe.

From the book Buzz: The Science and Lore of Alcohol and
Caffeine by Stephen Braun, 1996 (pg. 121) (ISBN
0-14-026845-6):

By a still imperfectly understood mechanism, cigarette smoking "revs up" the
liver's caffeine-destroying enzymatic machinery (Benowitz et al. 1989). As a
result, the half-life of caffeine among smokers is reduced to an average of
three hours (Parsons and Neims 1978). This double-speed elimination of caffeine
may explain the long-standing observation that smokers drink more coffee than
nonsmokers. Smokers may simply be adjusting their caffeine intake to maintain
the same degree of stimulation achieved by nonsmokers.